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United States Patent |
6,122,153
|
Becker
|
September 19, 2000
|
Temperature protection control for a motor starter
Abstract
A motor starter temperature protection control in which an ambient
temperature sensor is positioned on an inside cover of the motor starter
to sense ambient temperature across the power poles and heat sinks and
provide an ambient temperature signal indicative of the ambient
temperature in the motor starter enclosure. A power pole temperature
sensor is positioned in thermal communication with each power pole and
produce pole temperature signals indicative of the temperature of each
power pole. A microprocessor is connected to each of the temperature
sensors and receives the ambient temperature and the pole temperature
signals to control the motor starter operation based on the temperature
inputs. The microprocessor is programmed to periodically monitor the
ambient and power pole temperature signals and compare these signals
against a fan-on limit, and if the signals exceed the fan-on limit, the
control turns on the internal fans of the motor starter. The control
continues to monitor the ambient and power pole temperatures and if either
should exceed a maximum temperature limit, the motor starter is placed in
a motor shutdown mode, unless an optional temperature override has been
set. Upon motor shutdown, the control continues to monitor temperatures
and track how long it takes for the motor starter to cool down, and if it
takes too long to cool down, a maintenance flag is set to indicate that
cleaning or preventive maintenance is required.
Inventors:
|
Becker; James A. (Grafton, WI)
|
Assignee:
|
Eaton Corporation (Cleveland, OH)
|
Appl. No.:
|
270293 |
Filed:
|
March 15, 1999 |
Current U.S. Class: |
361/25; 361/103 |
Intern'l Class: |
H02H 005/04 |
Field of Search: |
361/23,25,93.8,103
318/641,806,783
|
References Cited
U.S. Patent Documents
4207602 | Jun., 1980 | Kussy et al. | 361/24.
|
5220478 | Jun., 1993 | Innes et al. | 361/93.
|
5680025 | Oct., 1997 | Bowers, III et al. | 318/806.
|
Primary Examiner: Sherry; Michael J.
Attorney, Agent or Firm: Boyle Fredrickson Ziolkowski S.C., Zande; Larry Vande
Claims
What is claimed is:
1. A motor starter temperature protection control comprising:
an ambient temperature sensor to sense ambient temperature and provide an
ambient temperature signal indicative of a temperature in a motor starter
enclosure;
at least one pole temperature sensor in thermal communication with an
electrically conducting bus in a motor starter and producing a pole
temperature signal indicative of a temperature of the electrically
conducting bus;
a processing unit connected to the ambient temperature sensor and the at
least one pole temperature sensor, the processing unit programmed to:
periodically monitor the ambient temperature signal and the pole
temperature signal;
compare the ambient temperature signal to a maximum temperature limit;
compare the pole temperature signal to a maximum temperature limit; and
produce a fault signal if one of the ambient temperature and the pole
temperature signals exceeds the maximum temperature limits.
2. The control of claim 1 wherein the processing unit is further programmed
to turn on a fan only when either the ambient temperature signal or the
pole temperature signal exceeds a fan-on limit and turns the fan off when
either the ambient temperature signal or the pole temperature signal falls
below the fan-on limit.
3. The control of claim 1 further comprising:
a display device connected to the processing unit to display an external
warning indicating an overheat condition;
a user input capable of selecting an override mode; and
wherein the processing unit is further programmed to shutdown a motor and
activate the display device when a fault signal is produced, and only
activate the display device if the override mode is selected from the user
input and not shutdown the motor when a fault signal is produced.
4. The control of claim 1 further comprising:
a motor starter having three power poles, each power pole having a heat
sink thereon and a fan in thermal communication with the heat sink;
three pole temperature sensors, each sensor in thermal communication with a
power pole of the motor starter and producing first, second, and third
pole temperature signals; and
wherein the processing unit is further programmed to:
determine a 1-2 deviation between the first and second pole temperature
signals;
determine a 2-3 deviation between the second and third pole temperature
signals;
determine a 1-3 deviation between the first and third pole temperature
signals;
compare the 1-2, 2-3, and 1-3 deviations to a pole temperature deviation
limit; and
produce a temperature deviation fault if any of the 1-2, 2-3, and 1-3
deviations exceed the pole temperature deviation limit.
5. The control of claim 4 further comprising:
an alarm indicator output to receive the temperature deviation fault and
produce an alarm indication when the temperature deviation fault is
present; and
a user override input that when active overrides motor shutdown when a
fault signal is present.
6. The control of claim 1 wherein the processing unit is further programmed
to:
track motor cool down by periodically reading the ambient temperature
signal and the pole temperature signal;
create an ambient temperature profile and a pole temperature profile based
on the ambient temperature signals and the pole temperature signals read
during the motor cool down;
compare the ambient temperature profile and the pole temperature profile to
a cool down limit; and
produce a maintenance indication if one or both of the ambient temperature
profile and the pole temperature profile exceeds the cool down limit.
7. The control of claim 6 wherein the processing unit is further programmed
to:
create an original ambient cool down profile and an original pole
temperature profile; and
compare the original ambient cool down profile and original pole
temperature profile to a present state ambient cool down profile and a
pole temperature profile.
8. A motor starter temperature protection control comprising:
an ambient temperature sensor to sense ambient temperature and provide an
ambient temperature signal indicative of a temperature in a motor starter
enclosure;
at least one pole temperature sensor in thermal communication with an
electrically conducting bus and producing a pole temperature signal
indicative of a temperature of the electrically conducting bus;
a processing unit connected to the ambient temperature sensor and the at
least one pole temperature sensor, the processing unit programmed to:
periodically monitor and read the ambient temperature signal and the pole
temperature signal upon motor shutdown;
create an ambient temperature profile and a pole temperature profile based
on the ambient temperature signals and the pole temperature signals read
during motor shutdown;
compare the ambient temperature profile and the pole temperature profile to
a cool down limit profile; and
produce a maintenance indication if one or both of the ambient temperature
profile and the pole temperature profile exceeds the cool down limit.
9. The control of claim 8 wherein the processing unit is further programmed
to:
create an original ambient cool down profile and an original pole
temperature profile; and
compare the original ambient cool down profile and original pole
temperature profile to a present state ambient cool down profile and a
pole temperature profile.
10. The control of claim 8 wherein the processing unit is further
programmed to:
periodically monitor the ambient temperature signal and the pole
temperature signal while in a motor run mode;
compare the ambient temperature signal to a maximum ambient temperature
limit;
compare the pole temperature signal to a maximum pole temperature limit;
and
produce a fault signal if one or both of the ambient temperature and the
pole temperature signals exceeds the maximum temperature limits.
11. The control of claim 10 wherein the processing unit is further
programmed to turn on a fan only when either or both of the ambient
temperature signal or the pole temperature signal exceeds a fan-on limit
and turns the fan off when either the ambient temperature signal or the
pole temperature signal falls below the fan-on limit.
12. The control of claim 11 further comprising:
a display device connected to the processing unit to display an external
warning indicating an overheat condition;
a user input capable of selecting an override mode; and
wherein the processing unit is further programmed to shutdown a motor and
activate the display device when a fault signal is produced, and only
activate the display device if the override mode is selected from the user
input and not shutdown the motor when a fault signal is produced.
13. The control of claim 8 further comprising:
a motor starter having three power poles, each power pole having a heat
sink thereon and a fan in thermal communication with the heat sink;
three pole temperature sensors, each sensor in thermal communication with a
power pole of the motor starter and producing first, second, and third
pole temperature signals; and
wherein the processing unit is further programmed to:
determine a 1-2 deviation between the first and second pole temperature
signals;
determine a 2-3 deviation between the second and third pole temperature
signals;
determine a 1-3 deviation between the first and third pole temperature
signals;
compare the 1-2, 2-3, and 1-3 deviations to a pole temperature deviation
limit; and
produce a temperature deviation fault if any of the 1-2, 2-3, and 1-3
deviations exceed the pole temperature deviation limit.
14. The control of claim 13 further comprising:
an alarm indicator output to receive the temperature deviation fault and
produce an alarm indication when the temperature deviation fault is
present; and
a user override input that when active overrides motor shutdown when a
fault signal is present.
15. A method of tracking temperature in a motor starter and controlling the
motor starter based on the temperature tracking comprising the steps of:
periodically monitoring an ambient temperature and a pole temperature of
each pole in a motor starter;
comparing the ambient temperature to a maximum ambient temperature and
producing a fault indication if the ambient temperature exceeds the
maximum ambient temperature;
comparing each pole temperature to a maximum pole temperature and producing
a fault if any pole temperature exceeds the maximum pole temperature;
determining any temperature deviation between poles in a multi-pole motor
starter; and
producing a temperature deviation fault if any temperature deviation
between poles exceeds a pole temperature deviation limit.
16. The method of claim 15 further comprising the step of turning on a fan
only when the ambient temperature, the pole temperature, or both, exceeds
a fan-on limit.
17. The method of claim 15 further comprising the steps of:
preventing continued motor operation when a fault is produced and
generating a noticeable indication when a fault occurs; and
providing a system override to disable shutting the motor down when a fault
occurs and only producing the noticeable indication when the fault occurs.
18. The method of claim 15 further comprising the steps:
tracking motor cool down by periodically monitoring the ambient temperature
and the pole temperature after entering a motor shutdown mode;
creating ambient temperature and pole temperature profiles based on
continued readings of the ambient temperature and the pole temperature
after motor shutdown as the motor starter cools;
comparing the ambient temperature profile and the pole temperature profile
to a cool down limit profile; and
producing a maintenance indication if either or both of the ambient
temperature or the pole temperature profiles exceeds the cool down limit.
19. The method of claim 1 further comprising the steps of:
creating an original ambient cool down profile and an original pole
temperature profile based on an ambient cool down temperature and a pole
cool down temperature during shutdown mode after the motor starter ran at
a first steady state operating temperature;
storing the original ambient cool down profile and the original pole
temperature profile in memory for later use during subsequent motor
starter cool downs; and
comparing a present state ambient cool down profile and a present state
pole temperature profile to the original ambient cool down profile and the
original pole temperature profile, respectively, to determine if
maintenance of the motor starter is required.
20. An apparatus for tracking temperature in a motor starter and
controlling the motor starter based on temperature tracking comprising:
means for periodically monitoring an ambient temperature and a pole
temperature of each pole in a motor starter;
means for comparing the ambient temperature to a maximum ambient
temperature and producing a fault indication if the ambient temperature
exceeds the maximum ambient temperature;
means for comparing each pole temperature to a maximum pole temperature and
producing a fault if any pole temperature exceeds the maximum pole
temperature;
means for determining any temperature deviation between poles in a
multi-pole motor starter; and
means for producing a temperature deviation fault if any temperature
deviation between poles exceeds a pole temperature deviation limit.
21. The apparatus of claim 20 further comprising a means for turning on a
fan only when any of the ambient temperature and the pole temperature
exceeds a fan-on limit.
22. The apparatus of claim 20 further comprising:
means for preventing continued motor operation when a fault is produced and
generating a noticeable indication when a fault occurs; and
means for providing a system override to disable motor shutdown when a
fault occurs and only producing the noticeable indication when the fault
occurs.
23. The apparatus of claim 20 further comprising:
means for tracking motor cool down by periodically monitoring the ambient
temperature and the pole temperature after entering a motor shutdown mode;
means for creating ambient temperature and pole temperature profiles based
on the ambient temperature and the pole temperature after motor shutdown
as the motor starter cools;
means for comparing the ambient temperature profile and the pole
temperature profile to a cool down limit; and
means for producing a maintenance indication if any of the ambient
temperature and the pole temperature profiles exceeds the cool down limit.
24. The apparatus of claim 20 further comprising:
means for creating an original ambient cool down profile and an original
pole temperature profile based on an ambient cool down temperature and a
pole cool down temperature during shutdown mode after the motor starter
ran a first time in a steady state operating temperature;
means for storing the original ambient cool down profile and the original
pole temperature profile in memory for continued use during subsequent
motor starter cool downs; and
means for comparing a present state ambient cool down profile and a present
state pole temperature profile to the original ambient cool down profile
and the original pole temperature profile, respectively, for determining
if maintenance of the motor starter is required.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to control systems for motor
starters, and more particularly to a method and apparatus to track
temperature in a motor starter and control the motor starter based on the
temperature tracking.
Many electrical devices use one form or another for thermal protection. One
of the most common forms of temperature protection includes the use of
thermistors, which are heat sensitive resistors that change resistive
value with temperature change. Typically, the thermistor is connected to
an electronic monitoring circuit which is set to react to a predetermined
resistance value. When that resistance value is reached, the electronic
monitoring circuit disconnects, or connects, the temperature protection
circuits, which then turn the device off. Most electrical devices use a
single thermistor for protection. Therefore, the level of protection
provided is solely dependent on the location of that single thermistor. In
other words, the thermal protection in reality protects only one small
portion of the device. In larger devices, many components can be damaged
before the thermal protection turns off the device. Another problem with
such systems is that they provide little warning or assistance in
diagnosing the cause of shutting down the device. Further, in some
applications or processes, it is critical that the electrical device not
be shutdown. In such processes, it would be desirable to have some
indication of an overheating condition while keeping the process running.
Another common method of thermal protection is the use of a bi-metal strip
or disk mounted within the device to open or close a circuit. Such devices
change shape with heat due to a differential thermal expansion between the
two metals that form the physical configuration. As the device changes
shape, it exerts a physical force on a switch, or on a set of contacts, to
change the state of an electrical circuit. That is, a normally opened
circuit, for example, will close to activate a temperature protection
circuit when the bi-metal strip deforms to a deflection point that
corresponds to a temperature indicating an overheating condition. This
form of thermal protection requires calibration by hand-bending or
tweaking for each particular device. Further, accuracy is suspect after
field adjustments are made and such bi-metal devices typically require
invasive connections between components, thereby reducing
manufactureability, increasing the cost of the component, and increasing
the overall size of the electrical equipment.
Although many electrical devices, including motor starters, may rely on
natural air convection for cooling, it is desirable to have some form of
forced air for sufficient cooling. Forced air requires either a fan or
blower to force the ambient air through or around the electrical device
for added cooling. Fans or blowers add yet another element to the device
that can fail without warning and decrease reliability of the equipment.
Further, keeping the fans running at all times, uses excess energy.
It would be desirable to have a thermal protection scheme that would
operate the fan only on an as-needed basis and provide some early
indication that the system is not functioning correctly, while providing a
device that protects the entire device efficiently and accurately.
SUMMARY OF THE INVENTION
The present invention provides a motor starter temperature protection
control that solves the aforementioned problems without adding significant
cost to the overall system.
A motor starter temperature protection control according to the present
invention includes an ambient temperature sensor positioned on an inside
cover of a motor starter to sense ambient temperature across the power
poles and heat sinks and provide an ambient temperature signal indicative
of the ambient temperature in the motor starter enclosure. A power pole
temperature sensor is positioned in thermal communication with each power
pole in the motor starter and produce pole temperature signals indicative
of the temperature of each power pole. A microprocessor is connected to
each of the temperature sensors and receives the ambient temperature
signal and the pole temperature signals to control the motor starter
operation based on the temperature inputs. The microprocessor is
programmed to periodically monitor the ambient and power pole temperature
signals and compare these signals against a fan-on limit, and if any of
these signals exceed the fan-on limit, the control turns on the internal
fans of the motor starter. The control continues to monitor the ambient
and power pole temperatures and if either should exceed a maximum
operating temperature limit, the motor starter is placed in a motor
shutdown mode, unless an optional temperature override has been set. Upon
motor shutdown, the control continues to monitor temperatures and track
how long it takes for the motor starter to cool down, and if it takes too
long to cool down, a maintenance flag is set to indicate that cleaning or
preventive maintenance is required.
In accordance with one aspect of the invention, A motor starter temperature
protection control includes an ambient temperature sensor to sense ambient
temperature and provide an ambient temperature signal indicative of a
temperature in a motor starter enclosure and at least one pole temperature
sensor in thermal communication with an electrically conducting bus in a
motor starter to produce a pole temperature signal indicative of a
temperature of the electrically conducting bus. A processing unit is
connected to the ambient temperature sensor and the pole temperature
sensor and programmed to periodically monitor the ambient temperature
signal and the pole temperature signal, compare the ambient temperature
signal to a maximum temperature limit, compare the pole temperature signal
to a maximum temperature limit, and then produce a fault signal if one of
the ambient temperature and the pole temperature signals exceeds the
maximum temperature limits.
In accordance with another aspect of the invention, a motor starter
temperature protection control includes an ambient temperature sensor to
sense ambient temperature and provide an ambient temperature signal
indicative of a temperature in a motor starter enclosure and at least one
pole temperature sensor in thermal communication with an electrically
conducting bus and producing a pole temperature signal indicative of a
temperature of the electrically conducting bus. A processing unit is
connected to the ambient temperature sensor and the one pole temperature
sensor and is programmed to periodically monitor and read the ambient
temperature signal and the pole temperature signal upon motor shutdown,
and create an ambient temperature profile and a pole temperature profile
based on the ambient temperature signals and the pole temperature signals
read during motor shutdown. The processor also compares the ambient
temperature profile and the pole temperature profile to a cool down limit
profile, and produces a maintenance indication if one or both of the
ambient temperature profile and the pole temperature profile exceeds the
cool down limit.
In accordance with yet another aspect of the invention, a method of
tracking temperature in a motor starter and controlling the motor starter
based on the temperature tracking includes periodically monitoring an
ambient temperature and a pole temperature of each pole in a motor starter
and comparing the ambient temperature to a maximum ambient temperature and
producing a fault indication if the ambient temperature exceeds the
maximum ambient temperature. The method also includes comparing each pole
temperature to a maximum pole temperature and producing a fault if any
pole temperature exceeds the maximum pole temperature. The method further
includes determining any temperature deviation between poles in a
multi-pole motor starter, and producing a temperature deviation fault if
any temperature deviation between poles exceeds a pole temperature
deviation limit.
Various other features, objects and advantages of the present invention
will be made apparent from the following detailed description and the
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The drawings illustrate the best mode presently contemplated for carrying
out the invention.
In the drawings:
FIG. 1 is a block diagram of a motor connected to a three-phase source
through a motor starter incorporating the present invention.
FIGS. 2A-2C is flow chart of the software as programmed in the
microprocessor of FIG. 1.
FIG. 3 is a flow chart subroutine as called for in the flow chart of FIG.
2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 is a block diagram of a motor starter temperature protection control
10 according to the present invention incorporated into a motor starter 12
controlling a motor 14 connected to a power source 15. Control 10 includes
a central processing unit 28, such as a microprocessor, a microcontroller,
a PLC, or any other device for electrical signal processing. The motor
starter temperature protection control 10 controls the function of the
motor starter 12 in an override manner based on the operating temperature
of the device. As shown in FIG. 1, the control 10 of the present invention
is shown in a three-phase motor starter application. In a manner that is
known, the motor starter 12 relays power from a three-phase source 15 to
the motor 14, in part by controlling coils 16, 18, and 20, and in part by
controlling a pair of SCRs (not shown) that are typically clamped between
two conducting bus bars, which is shown in block diagram form as pole A
22, pole B 24, and pole C 26.
The microprocessor 28 of the motor starter temperature protection control
10 receives input signals from a number of temperature sensors. In a
preferred embodiment, a temperature sensor is located on each power pole.
That is, temperature sensor A 30 is in thermal communication with power
pole A 22, temperature sensor B 32 is in thermal communication with power
pole B 24, and temperature sensor C 34 is in thermal communication with
power pole C 26. An ambient temperature sensor 36 is also located within
the motor starter 12 and connected to the microprocessor 28. In an
preferred embodiment, the ambient temperature sensor 36 is located in a
cover assembly between poles A and B or between poles B and C to sense the
ambient temperature within the housing enclosing motor starter 12. The
microprocessor 28 is also capable of receiving at least one input 38 for
the temperature protection control 10, which can be a dip-switch for
controlling whether the motor should be shutdown when a fault is detected
and display the fault on fault display 40, or whether to maintain the
motor operation and only display the fault on the fault display 40, for
use in critical processes.
The motor starter 12 also includes heat sinks 42, 44, and 46 mounted to
each power pole, 22, 24, and 26, respectively. Each power pole 22, 24, and
26 also has an associated fan 48, 50 and 52, respectively, to draw air
into the load side 54 of the motor starter 12 and move the air across each
heat sink 42, 44 and 46, and out a line side 56 of the motor starter 12.
The microprocessor 28 is connected to a fan driver 58, which in turn
drives the fans 48, 50 and 52. The microprocessor 28 also has output
control lines 60 for controlling the coils 16, 18, and 20 as well as
output control line 62 connected to control the SCRs of each pole 22, 24
and 26.
The operation of the control will now be described with reference to FIGS.
2-3. Referring to FIG. 2, the microprocessor is programmed, upon a start
command 64, to read the temperatures in the motor starter prior to
start-up of the motor at 66. The Read.sub.-- Temps is a subroutine and is
called a number of times in the main algorithm of FIG. 2, and is further
described with reference to FIG. 3.
Referring to FIG. 3, when the Read.sub.-- Temps 200 is called, the
microprocessor first reads the temperature of pole A 202 from the first
temperature sensor, and after converting the analog signal to a digital
signal and storing the result in memory 204, reads the temperature of pole
B 206, converts the analog signal to digital, and stores the result in
memory 208. The third temperature sensor is then read, acquiring the
temperature of pole C 210, which is then stored as a digital value 212.
The ambient temperature is read at 214, converted and stored at 216, and
the Read.sub.-- Temps subroutine returns 218 to the main algorithm of FIG.
2.
Referring back to FIG. 2, after the Read.sub.-- Temps 200 algorithm is
complete at 66, the initial values are saved at 68 and the motor is
allowed to start 70. That is, the temperature protection control of the
present invention relinquishes control of the motor starter to a main
control, which is not a subject of this invention.
Once the motor is up and running, the temperatures of the power poles and
the ambient are read 72, and if either the pole temperatures or the
ambient temperature exceeds a predetermined fan-on limit 74, 76, the fans
are turned on at 78. However, if the fan-on limit is not exceeded 74, 80,
the fans are kept off 81, and the temperatures are again read 72. The fans
are kept off as long as the pole temperatures and the ambient temperature
does not exceed the fan-on limit. After the fans are turned on 78, the
temperatures are read again at 82 and the temperatures of each of the
poles A, B, and C are compared to one another at 84 to determine what, if
any, deviation exists between poles A & B, B & C, and A & C. If any
deviation between the poles exceeds a predetermined limit 86, 88, a
temperature deviation fault flag is set and the fault is displayed 90.
A user temperature override bit is then checked at 92 to see whether or not
the user has ordered that the motor not be stopped because of an
overheating condition. If the temperature override bit has not been set
94, the system begins to shutdown the motor in an orderly manner 96.
However, if the temperature override bit has been set 92, 98, the system
continues back into the main algorithm to read the temperatures at 82.
After comparing the pole temperatures for deviations 84 and if there is no
deviation that exceeds the predetermined limit 86, 100, a maintenance flag
is cleared 102 and the pole temperatures and the ambient temperatures are
checked to see if they exceed a maximum temperature 104. If either the
ambient temperature or any of the pole temperatures exceed the maximum
temperature 104, 106, a maximum temperature fault flag is set and the
fault is displayed 108. The temperature override bit is checked 92, again,
if the bit has not been set 94, an orderly shutdown of the motor is begun
at 96. If the temperature override bit has been set 92, 98, then the
system continues to allow the motor to run and read the temperatures at
82.
If the system continues to run normally, that is, the pole temperatures do
not deviate 84, 86, 100 and neither the pole temperatures nor the ambient
temperatures exceeds a maximum temperature 104, 110, the maximum
temperature fault flag is checked to see if it is set 112. If it has 114,
then the flag is cleared 116 and the system continues to operate at 70. Of
course, this last loop will not occur unless the temperature override bit
is set at 92. If the maximum temperature fault flag had not been set 112,
118, then the system checks for a stop command 120. If none has occurred
122, the system returns to allowing the motor to run at 70. After reading
the temperature at 72, if the temperature has fallen below the limit to
keep the fans on 74, 80, the fans are turned off at 81 and the system
continues to operate as previously described.
However, once a stop command is received 120, 124, the proper and orderly
motor shutdown routine can begin 126, after which, the temperatures are
read again at 128 to develop a cool down profile 130. The control checks
the present temperatures 132, and as long as the motor starter has not yet
cooled down 134, the temperatures are periodically read and the system
stores in memory a cool down profile for each of the power poles and the
ambient.
Once the system has cooled down 132, 135, if this was the first time the
device was run and is shutting down only after reaching a steady state
operating temperature 136, 138, then the cool down profile is stored as
the original cool down profile for the device at 140 and the control then
waits for another start command 142. After the first steady state
operation of the device 136, 144, the cool down profile developed at 130
is stored as the present cool down profile 146. The present cool down
profile is then compared to the original cool down profile 148, and if a
deviation between the present cool down profile and the original cool down
profile exceeds a predetermined limit 150, 152, then a maintenance flag is
set 154 indicating that some corrective measure needs to be taken. For
example, a slow cool down can indicate low air flow that may be due to one
or more fans not operating correctly, the fan bearings may be degrading,
the heat sinks require cleaning, or the air inlet and/or air outlet in the
motor starter may be blocked. If there is no excessive deviation between
the cool down profiles 150, 156, the maintenance flag is cleared 158 and
the system waits for a next start command 142.
The present invention has been described in terms of the preferred
embodiment, and it is recognized that equivalents, alternatives, and
modifications, aside from those expressly stated, are possible and within
the scope of the appending claims.
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